Sampling system

ABSTRACT

A sampling system for and a method of separating a volume from a flow of a gaseous sample, the sampling system comprising: a first flow channel; a second flow channel intersecting the first flow channel; a first port in the first flow channel on one side of the point of intersection of the first and second flow channels through which a flow of a gaseous sample is in use delivered; a second port in the second flow channel on one side of the point of intersection of the first and second flow channels through which a flow of a carrier gas is in use delivered; a third port in one of the first and second flow channels on the other side of the point of intersection of the first and second flow channels through which a volume, as a sample plug, separated from the gaseous sample flow is in use driven; a fourth port in the other of the first and second flow channels to which a principal flow of the gaseous sample is in use directed; and a control unit to control the flow of the carrier gas delivered to the second port such as to separate a volume, as a sample plug, from the gaseous sample flow.

The present invention relates to a sampling system, preferably as amicrofabricated chip-based unit, for and a method of separating avolume, as a sample plug, from a flow of a gaseous sample, and to ameasurement system incorporating the sampling system. In particular, thepresent invention relates to a sampling system for and a method ofseparating a volume, as a sample plug, from a flow of a gaseous samplefor delivery to the separation column of a measurement system such as agas chromatograph. In the context of the present invention the termgaseous sample is to be understood as encompassing gases andsupercritical fluids.

Precisely metered volumes of fluid samples, typically very small volumesof up to 2 μl, are required by many measurement systems, such as gas andliquid chromatographs, for accurate sample analysis.

Microsyringes are commonly used to deliver metered volumes of fluidsamples, either as gases or liquids. These syringes, however, have alimited volumetric accuracy, and as such are not suited to the deliveryof very small volumes.

Minaturized chip-based sampling systems have been proposed, but thesesystems are complex and require moving components to valve and meter afluid sample. As will be appreciated, the fabrication of systemsincluding such minaturized components is particularly difficult, and inrequiring moving parts can suffer from problems of reliability.

It is thus an aim of the present invention to provide an improvedsampling system, preferably as a microfabricated chip-based samplingunit, for separating a small volume, as a sample plug, from a flow of agaseous sample, and in particular a sampling system which requires nomoving parts. It is also an aim of the present invention to provide animproved sampling method.

Accordingly, the present invention provides a sampling system forseparating a volume, as a sample plug, from a flow of a gaseous sample,comprising: a first flow channel; a second flow channel intersecting thefirst flow channel; a first port in the first flow channel on one sideof the point of intersection of the first and second flow channelsthrough which a flow of a gaseous sample is in use delivered; a secondport in the second flow channel on one side of the point of intersectionof the first and second flow channels through which a flow of a carriergas is in use delivered; a third port in one of the first and secondflow channels on the other side of the point of intersection of thefirst and second flow channels through which a volume, as a sample plug,separated from the gaseous sample flow is in use driven; a fourth portin the other of the first and second flow channels on the other side ofthe point of intersection of the first and second flow channels to whicha principal flow of the gaseous sample is in use directed; and a controlunit operably configured to control the flow of the carrier gasdelivered to the second port such as to separate a volume, as a sampleplug, from the gaseous sample flow.

In one embodiment the third port is in the first flow channel and thefourth port is in the second flow channel, and the control unit isconfigured to interrupt the flow of the carrier gas to the second portto separate a volume, as a sample plug, from the gaseous sample flow.

Preferably, the control unit is configured to interrupt the flow of thecarrier gas to the second port for a predetermined period of time, withthe period of interruption determining the volume of the separatedsample plug for a given flow rate.

In another embodiment the third port is in the second flow channel andthe fourth port is in the first flow channel, and the control unit isconfigured to deliver a high flow of the carrier gas to the second portto separate a volume, as a sample plug, from the gaseous sample flow.

Preferably, the sampling system further comprises a fifth port in thesecond flow channel on the other side of the point of intersection ofthe first and second flow channels through which a further flow of thecarrier gas is in use delivered, wherein the control unit is configuredin a first state to deliver the first and further flows of the carriergas through the respective ones of the second and fifth ports and in asecond, sampling state to deliver a high flow of the carrier gas to thesecond port to separate a volume, as a sample plug, from the gaseoussample flow.

Preferably, the first and second flow channels intersect one anothersubstantially orthogonally.

In one embodiment the first flow channel includes first and secondsections connected at a single point along the length of the second flowchannel.

In another embodiment the first flow channel includes first and secondsections connected at respective ones of spaced points along the lengthof the second flow channel.

Preferably, the sampling system further comprises a substrate chip inwhich the flow channels and the ports are defined.

The present invention also extends to a measurement system incorporatingthe above-described sampling system.

The present invention also provides a method of separating a volume, asa sample plug, from a flow of a gaseous sample, comprising the steps of:providing a sampling system comprising a first flow channel, a secondflow channel intersecting the first flow channel, a first port in thefirst flow channel on one side of the point of intersection of the firstand second flow channels, a second port in the second flow channel onone side of the point of intersection of the first and second flowchannels, a third port in one of the first and second flow channels onthe other side of the point of intersection of the first and second flowchannels, and a fourth port in the other of the first and second flowchannels on the other side of the point of intersection of the first andsecond flow channels; flowing a gaseous sample from the first port tothe fourth port; and applying a flow of a carrier gas to the second portsuch as to separate a volume, as a sample plug, from the gaseous sampleflow and drive the separated sample plug to the third port.

In one embodiment the third port is in the first flow channel and thefourth port is in the second flow channel, and a flow of the carrier gasto the second port is interrupted to separate a volume, as a sampleplug, from the gaseous sample flow.

Preferably, the flow of the carrier gas is interrupted for apredetermined period of time, with the period of interruptiondetermining the volume of the sample plug for a given flow rate.

In another embodiment the third port is in the second flow channel andthe fourth port is in the first flow channel, and a high flow of thecarrier gas is delivered to the second port to separate a volume, as asample plug, from the gaseous sample flow.

Preferably, the sampling system further comprises a fifth port in thesecond flow channel on the other side of the point of intersection ofthe first and second flow channels, and the sampling method furthercomprises the step of applying a flow of the carrier gas to the fifthport, first and further substantially similar flows of the carrier gasbeing delivered in a first state through the respective ones of thesecond and fifth ports and in a second, sampling state a high flow ofthe carrier gas being delivered to the second port to separate a volume,as a sample plug, from the gaseous sample flow.

Preferably, the first and second flow channels intersect one anothersubstantially orthogonally.

In one embodiment the first flow channel includes first and secondsections connected at a single point along the length of the second flowchannel.

In another embodiment the first flow channel includes first and secondsections connected at respective ones of spaced points along the lengthof the second flow channel.

Preferably, the sampling system further comprises a substrate chip inwhich the flow channels and the ports are defined.

Preferably, the carrier gas is an inert gas.

Preferred embodiments of the present invention will now be describedhereinbelow by way of example only with reference to the accompanyingdrawings, in which:

FIG. 1 schematically illustrates a microfabricated chip-based samplingsystem in accordance with a first embodiment of the present invention;

FIGS. 2(a) to (c) schematically illustrate the operation of the samplingsystem of FIG. 1;

FIG. 3 schematically illustrates a microfabricated chip-based samplingsystem in accordance with a second embodiment of the present invention;

FIGS. 4(a) and (b) schematically illustrate the operation of thesampling system of FIG. 3;

FIG. 5 schematically illustrates a microfabricated chip-based samplingsystem in accordance with a third embodiment of the present invention;

FIG. 6 schematically illustrates a further embodiment of amicrofabricated chip-based sampling system in accordance with anotherexample; and

FIG. 7 illustrates spectral samples varying with time illustrating theforming of gas samples using the system of FIG. 6.

FIG. 1 illustrates a sampling system in accordance with a firstembodiment of the present invention.

The sampling system comprises a microfabricated substrate chip 2 whichincludes a first channel 4, in this embodiment a linear channel, whichincludes first and second ports 6, 8, and a second channel 10, in thisembodiment a linear channel, which intersects the first channel 4 andincludes first and second ports 12, 14. In an alternative embodiment thefirst and second channels 4, 10 can be meandering channels whichpreferably include a plurality of bends. Preferably, the first andsecond channels 4, 10 each have a width of from about 50 to 300 μm and adepth of from about 10 to 40 μm.

The chip 2 is fabricated from two plates, which, in this embodiment, arecomposed of microsheet glass. In a first step, one of the plates isetched by HF wet etching to form wells which define the first and secondchannels 4, 10, with the wells having the dimensions mentioned above. Ina second step, four holes are drilled, in this embodiment by ultrasonicvibration, into the other plate so as to provide the ports 6, 8 of thefirst channel 4 and the ports 12, 14 of the second channel 10. In athird and final step, the two plates are bonded together by directfusion bonding.

The sampling system further comprises a sample delivery line 17 whichincludes a metering valve 18 and is connected to the first port 6 of thefirst channel 4, in this embodiment by a Swagelok™ connector to a fusedsilica capillary tube bonded to the chip 2, through which a controlledflow of a gaseous sample is in use introduced.

The sampling system further comprises a sample plug supply line 19 whichis connected to the second port 8 of the first channel 4, in thisembodiment by a Swagelok™ connector to a fused silica capillary tubebonded to the chip 2, through which a metered volume of the gaseoussample, as a sample plug, is in use fed to the separation column of ameasurement system.

The sampling system further comprises a carrier gas supply Unit whichcomprises a carrier gas supply 20, in this embodiment a pressurised gassource, and a carrier gas delivery line 21 which includes a meteringvalve 23 and connects the carrier gas supply 20 to the first port 12 ofthe second channel 10, in this embodiment by a Swagelok™ connector to afused silica capillary tube bonded to the chip 2, through which acontrolled flow of a carrier gas is in use delivered. In this embodimentthe carrier gas is an inert gas such as helium.

The sampling system further comprises a waste line 26 which includes avacuum pump 28 and is connected to the second port 14 of the secondchannel 10, in this embodiment by a Swagelok™ connector to a fusedsilica capillary tube bonded to the chip 2, through which flows of thegaseous sample and the carrier gas are selectively fed from the chip 2.In this embodiment the vacuum pump 28 is provided to maintain a reducedpressure in the downstream section of the second channel 10 relative tothe pressure in the downstream section of the first channel 4. In analternative embodiment, however, the vacuum pump 28 could be omitted andinstead the shape and/or dimension of the downstream sections of thefirst and second channels 4, 10 configured such that, for a givenpressure of the delivered flow of the carrier gas, the pressure in thedownstream section of the second channel 10 is sufficiently lower thanthe pressure in the downstream section of the first channel 4 as tocause the flow of the gaseous sample to be directed to waste through thedownstream section of the second channel 10.

The sampling system further comprises a control unit 30 which isconnected to the valve 18 in the sample delivery line 17, the valve 23in the carrier gas delivery line 21 and the vacuum pump 28 in the wasteline 26 such as to allow for the control of the flow rates of thegaseous sample and the carrier gas to the respective ones of the inletports 6, 12 of the first and second channels 4, 10 and the pressure atthe outlet port 14 of the second channel 10. The function of the controlunit 30 will become clear from the following description of theoperation of the sampling system.

In operation, a continuous flow of a gaseous sample is maintained to theinlet port 6 of the first channel 4. In maintaining a continuous flowthrough the chip 2, the sampling system finds particular application incontinuous gas monitoring.

In a standby or non-sampling mode, the flow of the gaseous sample isdirected entirely to waste through the outlet port 14 of the secondchannel 10 as illustrated in FIG. 2(a). In this embodiment the flow ofthe gaseous sample to waste is achieved both by controlling the vacuumpump 28 such as to maintain a reduced pressure at the outlet port 14 ofthe second channel 10 as compared to the pressure at the outlet port 8of the first channel 4 and controlling the valves 18, 23 in the deliverylines 17, 21 such as to maintain the carrier gas at a higher pressurethan the gaseous sample. The flow of the gaseous sample is caused to bediverted into the downstream section of the second channel 10 by thecombination of the effect of the reduced pressure in the downstreamsection of the second channel 10 relative to that in the downstreamsection of the first channel 4 and the action of the flow of thehigher-pressure carrier gas which flows orthogonally to the flow of thelower-pressure gaseous sample in the first channel 4. In this embodimentthe pressure of the delivered carrier gas is such as to maintain, inaddition to a flow through the downstream section of the second channel10, a flow through the downstream section of the first channel 4. Thisflow of carrier gas through the downstream section of the first channel4 is particularly advantageous in that the communication path to theseparation column is continuously flushed, thereby preventing thepossible situation of sample molecules diffusing from the flow of thegaseous sample into the gaseous environment in communication with theseparation column.

In a sample plug injection mode, the valve 23 in the carrier gasdelivery line 21 is, under the control of the control unit 30, closedfor a predetermined period of time. While the valve 23 in the carriergas delivery line 21 is closed, the gaseous sample continues aspreviously to flow through the downstream section of the second channel10, but also now flows into the downstream section of the first channel4; flow into the upstream section of the second channel 10 beingprevented by the back pressure of the carrier gas remaining therein.This flow into the downstream section of the first channel 4 isillustrated in FIG. 2(b). On opening the valve 23 in the carrier gasdelivery line 21, a small plug of the gaseous sample is separated fromthe main flow of the gaseous sample by the knife-like action of thehigher-pressure carrier gas flow. This separation of a sample plug isillustrated in FIG. 2(c). The volume of the sample plug is determined bythe dimensions of the channels 4, 10, the injection period and the flowrates of the gaseous sample and the carrier gas. This separated sampleplug is then driven by the flow of the carrier gas through thedownstream section of the first channel 4 to the separation column.

FIG. 3 illustrates a sampling system in accordance with a secondembodiment of the present invention.

The sampling system comprises a microfabricated substrate chip 102 whichincludes a first channel 104, in this embodiment a linear channel, whichincludes first and second ports 106, 108, a second channel 110, in thisembodiment a linear channel, which intersects the first channel 104 andincludes first and second ports 112, 114, and a third channel 115 whichincludes a port 116 and is connected to the second channel 110 at apoint between the point of intersection of the first and second channels104, 110 and the second port 114 of the second channel 110. In analternative embodiment the first and second channels 104, 110 can bemeandering channels which include a plurality of bends. Preferably, thefirst, second and third channels 104, 110, 115 each have a width of fromabout 50 to 300 μm and a depth of from about 10 to 40 μm.

In the same manner as the above-described first embodiment, the chip 102is fabricated from two plates which are composed of microsheet glass. Ina first step, one of the plates is etched by HF wet etching to formwells which define the first, second and third channels 104, 110, 115,with the wells having the dimensions mentioned above. In a second step,four holes are drilled, in this embodiment by ultrasonic vibration, intothe other plate so as to provide the ports 106, 108 of the first channel104, the ports 112, 114 of the second channel 110 and the port 116 ofthe third channel 115. In a third and final step, the two plates arebonded together by direct fusion bonding.

The sampling system further comprises a sample delivery line 117 whichincludes a metering valve 118 and is connected to the first port 106 ofthe first channel 104, in this embodiment by a Swagelok™ connector to afused silica capillary tube bonded to the chip 102, through which acontrolled flow of a gaseous sample is in use introduced.

The sampling system further comprises a sample plug supply line 119which is connected to the second port 114 of the second channel 110, inthis embodiment by a Swagelok™ connector to a fused silica capillarytube bonded to the chip 102, through which a metered volume of thegaseous sample, as a sample plug, is in use fed to the separation columnof a measurement system.

The sampling system further comprises a carrier gas supply unit whichcomprises a carrier gas supply 120, in this embodiment a pressurised gassource, and first and second carrier gas delivery lines 121, 122 whicheach include a metering valve 123, 124 and connect the carrier gassupply 120 to respective ones of the first port 112 of the secondchannel 110 and the port 116 of the third channel 115, in thisembodiment by Swagelok™ connectors to fused silica capillary tubesbonded to the chip 102, through which separate controlled flows of thecarrier gas are in use delivered. In this embodiment the carrier gas isan inert gas such as helium.

The sampling system further comprises a waste line 126 which includes avacuum pump 128 and is connected to the second port 108 of the firstchannel 104, in this embodiment by a Swagelok™ connector to a fusedsilica capillary tube bonded to the chip 102, through which flows of thegaseous sample and the carrier gas are selectively fed from the chip102. In this embodiment the vacuum pump 28 is provided to maintain areduced pressure in the downstream section of the first channel 104.

The sampling system further comprises a control unit 130 which isconnected to the valve 118 in the sample delivery line 117, the valves123, 124 in the carrier gas delivery lines 121, 122 and the vacuum pump128 in the waste line 126 such as to allow for the control of the flowrates of the gaseous sample and the carrier gas to the respective onesof the inlet ports 106, 112, 116 of the first, second and third channels104, 110, 115 and the pressure at the outlet port 108 of the firstchannel 104. The function of the control unit 130 will become clear fromthe following description of the operation of the sampling system.

Operation of the sampling system for batch sampling is as follows.

In a first step, under the control of the control unit 130, the valves123, 124 in the carrier gas delivery lines 121, 122 are configured suchthat a relatively low flow of carrier gas is delivered therethrough soas to maintain a flow of carrier gas through each of the sections of thesecond channel 110 towards the intersection thereof with the firstchannel 104, the valve 118 in the sample delivery line 117 is configuredto provide a flow of a gaseous sample through the first channel 104, andthe vacuum pump 128 is configured to provide a reduced pressure at theoutlet port 108 of the first channel 104. With this configuration, asillustrated in FIG. 4(a), the flow of the gaseous sample is entirelythrough the first channel 104, with the carrier gas flows preventing theflow of the gaseous sample into either of the sections of the secondchannel 110. As illustrated in FIG. 4(a), the carrier gas flows areexhausted with the flow of the gaseous sample to waste, in partsheathing the flow of the gaseous sample. The flow of carrier gasthrough the downstream section of the second channel 110 is particularlyadvantageous in that the downstream section of the second channel 110which is connected to the separation column is continuously flushed,thereby preventing the possible situation of sample molecules diffusingfrom the flow of the gaseous sample into the gaseous environment incommunication with the separation column.

In a second, sample plug injection step, under the control of thecontrol unit 130, the valve 123 in the first carrier gas delivery line121 is configured such that a relatively high flow of the carrier gas isdelivered therethrough, with the relatively low flow of the carrier gasbeing maintained through the second carrier gas delivery line 122. Thishigh flow of carrier gas separates the plug of the gaseous sample at theintersection of the first and second channels 104, 110, and drives thatseparated sample plug through the downstream section of the secondchannel 110 to the separation column, and at the same time flows intothe sections of the first channel 104 so as to prevent the introductionof any further of the gaseous sample. This separation and flow into thedownstream section of the second channel 110 is illustrated in FIG.4(b). The volume of the sample plug is determined by the dimensions ofthe first and second channels 104, 110 and the relative pressures of thecarrier gas flows which act to consain and thus squeeze the flow of thegaseous sample at the intersection of the first and second channels 104,110.

FIG. 5 illustrates a sampling system in accordance with a thirdembodiment of the present invention.

This sampling system is almost identical to that of the above-describedsecond embodiment, and thus in order to avoid unnecessary duplication ofdescription only the differences will be described in detail, with likeparts being designated by like reference signs. This sampling systemdiffers only in that the first channel 104 is non-linear and includesfirst and second sections 104 a, 104 b connected to the second channel110 at spaced points. By spacing the first and second sections 104 a,104 b of the first channel 104, the volume of the gaseous sample in thesecond channel 110, which defines the sample plug, is greater ascompared to that in the second-described embodiment where the firstchannel 104 is a linear channel. As will be understood, the volume ofthe sample plug can be increased by increasing the spacing or offset ofthe first and second sections 104 a, 104 b of the first channel 104.Operation of this sampling system is the same as for thesecond-described embodiment.

FIG. 6 illustrates a further example sampling system similar to that ofFIG. 5.

FIG. 7 illustrates the variation of observed spectral data at a sampleoutput of the system of FIG. 6 demonstrating the sampling operation.

Finally, it will be understood that the present invention has beendescribed in its preferred embodiments and can be modified in manydifferent ways without departing from the scope of the invention asdefined by the appended claims.

For example, although the preferred embodiments are based onmicrofabricated substrate chips 2, 102, these substrate chips could bereplaced by large scale components as fabricated from tubing or machinedcomponents.

1. A sampling system for separating a volume, as a sample plug, from aflow of a gaseous sample, comprising: a first flow channel; a secondflow channel intersecting the first flow channel; a first port in thefirst flow channel on one side of the point of intersection of the firstand second flow channels through which a flow of a gaseous sample is inuse delivered; a second port in the second flow channel on one side ofthe point of intersection of the first and second flow channels throughwhich a flow of a carrier gas is in use delivered; a third port in oneof the first and second flow channels on the other side of the point ofintersection of the first and second flow channels through which avolume, as a sample plug, separated from the gaseous sample flow is inuse driven; a fourth port in the other of the first and second flowchannels on the other side of the point of intersection of the first andsecond flow channels to which a principal flow of the gaseous sample isin use directed; and a control unit operably configured to control theflow of the carrier gas delivered to the second port such as to separatea volume, as a sample plug, from the gaseous sample flow.
 2. Thesampling system of claim 1, wherein the third port is in the first flowchannel and the fourth port is in the second flow channel, and thecontrol unit is configured to interrupt the flow of the carrier gas tothe second port to separate a volume, as a sample plug, from the gaseoussample flow.
 3. The sampling system of claim 2, wherein the control unitis configured to interrupt the flow of the carrier gas to the secondport for a predetermined period of time, with the period of interruptiondetermining the volume of the separated sample plug.
 4. The samplingsystem of claim 1, wherein the third port is in the second flow channeland the fourth port is in the first flow channel, and the control unitis configured to deliver a high flow of the carrier gas to the secondport to separate a volume, as a sample plug, from the gaseous sampleflow.
 5. The sampling system of claim 4, further comprising a fifth portin the second flow channel on the other side of the point ofintersection of the first and second flow channels through which afurther flow of the carrier gas is in use delivered, wherein the controlunit is configured in a first state to deliver the first and furtherflows of the carrier gas through the respective ones of the second andfifth ports and in a second, sampling state to deliver a high flow ofthe carrier gas to the second port to separate a volume, as a sampleplug, from the gaseous sample flow.
 6. The sampling system of any ofclaims 1 to 5, wherein the first and second flow channels intersect oneanother substantially orthogonally.
 7. The sampling system of any ofclaims 1 to 6, wherein the first flow channel includes first and secondsections connected at a single point along the length of the second flowchannel.
 8. The sampling system of any of claims 1 to 6, wherein thefirst flow channel includes first and second sections connected atrespective ones of spaced points along the length of the second flowchannel.
 9. The sampling system of any of claims 1 to 8, wherein thesampling system further comprises a substrate chip in which the flowchannels and the ports are defined.
 10. A measurement systemincorporating the sampling system of any of claims 1 to
 9. 11. A methodof separating a volume, as a sample plug, from a flow of a gaseoussample, comprising the steps of: providing a sampling system comprisinga first flow channel, a second flow channel intersecting the first flowchannel, a first port in the first flow channel on one side of the pointof intersection of the first and second flow channels, a second port inthe second flow channel on one side of the point of intersection of thefirst and second flow channels, a third port in one of the first andsecond flow channels on the other side of the point of intersection ofthe first and second flow channels, and a fourth port in the other ofthe first and second flow channels on the other side of the point ofintersection of the first and second flow channels; flowing a gaseoussample from the first port to the fourth port; and applying a flow of acarrier gas to the second port such as to separate a volume, as a sampleplug, from the gaseous sample flow and drive the separated sample plugto the third port.
 12. The method of claim 11, wherein the third port isin the first flow channel and the fourth port is in the second flowchannel, and a flow of the carrier gas to the second port is interruptedto separate a volume, as a sample plug, from the gaseous sample flow.13. The method of claim 12, wherein the flow of the carrier gas isinterrupted for a predetermined period of time, with the period ofinterruption determining the volume of the sample plug.
 14. The methodof claim 11, wherein the third port is in the second flow channel andthe fourth port is in the first flow channel, and a high flow of thecarrier gas is delivered to the second port to separate a volume, as asample plug, from the gaseous sample flow.
 15. The method of claim 14,wherein the sampling system further comprises a fifth port in the secondflow channel on the other side of the point of intersection of the firstand second flow channels, and further comprising the step of applying aflow of the carrier gas to the fifth port, first and furthersubstantially similar flows of the carrier gas being delivered in afirst state through the respective ones of the second and fifth portsand in a second, sampling state a high flow of the carrier gas beingdelivered to the second port to separate a volume, as a sample plug,from the gaseous sample flow.
 16. The method of any of claims 11 to 15,wherein the first and second flow channels intersect one anothersubstantially orthogonally.
 17. The method of any of claims 11 to 16,wherein the first flow channel includes first and second sectionsconnected at a single point along the length of the second flow channel.18. The method of any of claims 11 to 16, wherein the first flow channelincludes first and second sections connected at respective ones ofspaced points along the length of the second flow channel.
 19. Themethod of any of claims 11 to 18, wherein the sampling system furthercomprises a substrate chip in which the flow channels and the ports aredefined.
 20. The method of any of claims 11 to 19, wherein the carriergas is an inert gas.
 21. A sampling system for separating a volume, as asample plug, from a flow of a gaseous sample substantially ashereinbefore described with reference to FIGS. 1 and 2, FIGS. 3 and 4and/or FIG. 5 of the accompanying drawings.
 22. A method of separating avolume, as a sample plug, from a flow of a gaseous sample substantiallyas hereinbefore described with reference to FIGS. 1 and 2, FIGS. 3 and 4and/or FIG. 5 of the accompanying drawings.